A build-up multilayer wiring board alternately has interlayer resin insulators and conductive circuit layers, provides holes to the interlayer resin insulator layers, and then electrically connects the upper layers and lower layers by forming conductive films on the surface of the walls of these holes.
A hole (via hole) in the interlayer resin insulating layer is generally formed with the use of an exposure and developing process, which gives photosensitive property to the interlayer resin.
However, the required diameter of these via holes in a multilayer printed wiring board is almost 100 μm or less, thus it is necessary to develop technology which makes it possible to maintain this small diameter. Due to such stringent requirements, the employment of a processing method utilizing a laser beam for the boring of the holes in the build-up multilayer wiring board will now be investigated.
Technology using laser for boring is proposed, in JPA HEI 3-54884. According to this method, a light beam from a laser source is received by a processing head for deflection. Thereby, the laser beam is irradiated to a predetermined resin insulator to form a hole.
In mass production of multi-layer printed wiring boards, which have hundreds to thousands of via holes in each layer, efficient hole drilling is essential. In addition, via holes need accurate positioning for electrical connection to conductor circuits in the layers below.
Unfortunately, it has been difficult to control, with high accuracy, the position of laser irradiation for via hole drilling in mass production. This has aroused a need for a process for fabricating a multi-layer printed wiring board containing openings at accurate positions. However, the current method of manufacture can not guarantee accurate positioning of laser irradiation. Improvement in positioning accuracy is offset by a necessary decrease in head driving speed, which in turn lowers productivity.
The present invention aims to address the above-mentioned problems. It is an object of the present invention to provide a process for producing a multi-layer printed wiring board, said process permitting accurate positioning of via holes independent of the accuracy of position for laser irradiation, thereby drilling a large number of holes efficiently by laser irradiation.
It is another object of the present invention to provide a method for increasing the driving speed of the scanning head without decreasing the accuracy of positions of via holes.